Multilayer Kirkpatrick-Baez focusing mirrors with phase compensation for sub-20 nm focusing at the hard X-ray nanoprobe beamline of SSRF.

The hard X-ray nanoprobe beamline is the first beamline to take advantage of the full coherent beam to attain the nanoscale focusing at the Shanghai Synchrotron Radiation Facility (SSRF). Here we introduce the beamline and specially go over the features of the multilayer Kirkpatrick-Baez focusing system and its supporting phase compensator system. The performance and stability of the phase compensator are also put to the test. By using the speckle scanning metrology, the wavefront of a focused beam was characterized and intensity distribution near the focus was reconstructed. The focusing performance was greatly enhanced by two phase compensations based on a global optimization technique, and a two-dimensional focal spot of 26 nm × 17 nm was achieved and maintained with good stability.

Analysis of partially coherent light propagation through the soft X-ray interference lithography beamline at SSRF.

The mutual optical intensity (MOI) model is extended to the simulation of the interference pattern produced by extreme ultraviolet lithography with partially coherent light. The partially coherent X-ray propagation through the BL08U1B beamline at Shanghai Synchrotron Radiation Facility is analysed using the MOI model and SRW (Synchrotron Radiation Workshop) method. The fringe intensity at the exposure area is not uniform but has similar envelope lines to Fresnel diffraction, which is explained by the diffraction from the finite grating modelled as a single aperture. By balancing the slit size and photon stop size, the fringe visibility, photon flux and intensity slope can be optimized. Further analysis shows that the effect of pink light on the aerial images is negligible, whereas the third-harmonic light should be considered to obtain a balance between high fringe visibility and high flux. Two grating interference exposure experiments were performed in the BL08U1B beamline. The aerial image depth showed that the polymethyl methacrylate photoresist depth was determined by the X-ray coherence properties.

Surface States in Ternary CdSSe Quantum Dot Solar Cells.

Ternary CdSSe quantum dot-sensitized solar cells (QDSCs) have demonstrated advantages such as wide absorption ranges and tunable band structures. However, the oxygen additives absorbed on such multicomponent quantum dot (QD) surfaces induce band bending at the TiO2/CdSSe interface and prevent charge transport in QDSCs, as determined via X-ray photoelectron spectroscopy (XPS) and synchrotron-based X-ray Absorption Near-Edge Structure (XANES) analysis. Annealing of TiO2/CdSSe QDs photoanodes was conducted at different temperatures under Ar atmospheres to eliminate oxygen additives and interfacial band bending. The short-circuit current (J(sc))of the annealed ternary CdSSe QDSCs is obviously improved, whereas the TiCl4 treatment and MgO coating of the TiO2 nanocrystals are assisted by the annealing to compensate for the loss of opencircuit voltage (V(oc)) and fill factor (FF). Ternary CdSSe QDSCs with efficiencies of 4.72% have been achieved using the optimized annealing conditions.

Numerical analysis of partially coherent radiation at soft x-ray beamline.

A new model for numerical analysis of partially coherent x-ray at synchrotron beamlines is presented. The model is based on statistical optics. Four-dimensional coherence function, Mutual Optical Intensity (MOI), is applied to describe the wavefront of the partially coherent light. The propagation of MOI through optical elements in the beamline is deduced with numerical calculation. The coherence of x-ray through beamlines can be acquired. We applied the model to analyze the coherence in the STXM beamline at SSRF, and got the coherence length of the beam at the endstation. To verify the theoretical results, the diffraction experiment of a single slit was performed and the diffraction pattern was simulated to get the coherence length, (31 ± 3.0) µm × (25 ± 2.1) µm (H × V), which had a good agreement with the theoretical results, (30.7 ± 0.6) µm × (31 ± 5.3) µm (H × V). The model is applicable to analyze the coherence in synchrotron beamlines.

Ma-PbFRET: multiple acceptors FRET measurement based on partial acceptor photobleaching.

Fluorescence resonance energy transfer (FRET) measurement based on partial acceptor photobleaching (PbFRET) is easy to implement without external references. However, the current PbFRET methods are inapplicable to the construct with multiple acceptors, which largely increase the Förster distance. Here, we proposed a linear theory for the dependence of the acceptor photobleaching probability of construct with multiple acceptors on the photobleaching degree (x) and developed a multiple acceptors PbFRET method (Ma-PbFRET) to measure the FRET efficiency of construct with multiple acceptors (n) by measuring the fluorescence intensities of both donor and acceptor channels before and after acceptor photobleaching. The Ma-PbFRET method was validated by measuring the FRET efficiency of construct with two or three acceptors under different x in living cells. Our experimental results demonstrate that the Ma-PbFRET method is capable of exactly quantifying the FRET efficiency of construct with multiple acceptors, providing a simple and powerful tool to investigate the assembly/disassembly of biomolecular complexes with larger distance in living cells.

Partial acceptor photobleaching-based quantitative FRET method completely overcoming emission spectral crosstalks.

Based on the quantitative fluorescence resonance energy transfer (FRET) method named PbFRET we reported recently, we herein developed a partial acceptor photobleaching-based quantitative FRET algorithm named B-PbFRET method. B-PbFRET overcomes not only the acceptor excitation crosstalk and donor emission spectral crosstalk but also the acceptor emission spectral crosstalk that harasses previous methods including fluorescence lifetime (FLIM), fluorescence recovery of donor after acceptor photobleaching, and acceptor sensitized emission (SE)-based methods. B-PbFRET method is implemented by simultaneously measuring the fluorescence intensity of both donor and acceptor channels at donor excitation before and after partial acceptor photobleaching, and it can directly measure the FRET efficiency (E) without any verified references. Based on the theoretical analysis of B-PbFRET, we also developed a more straightforward correction method named C-PbFRET to obtain the absolute E from the value measured by PbFRET for a given donor-acceptor pair. We validated both B-PbFRET and C-PbFRET methods by measuring the E of two linked constructs, 18AA and SCAT3 proteins, in single living cells, and our data demonstrated that both B-PbFRET and C-PbFRET methods can directly measure the absolute E of the linked constructs inside living cells under different degrees of acceptor emission spectral crosstalk.

Soft x-ray spectroscopic endstation at beamline 08U1A of Shanghai Synchrotron Radiation Facility.

A spectroscopic endstation with magnetic field, voltage, and low temperature control has been installed and commissioned at the soft X-ray beamline 08U1A of Shanghai Synchrotron Radiation Facility, which can obtain a magnetic field up to ±0.53 T, applied current and bias voltage, and cryogenic temperatures down to 14 K with a Gifford-McMahon cycle cryocooler. The endstation can perform soft X-ray absorption spectroscopy methods including total electron yield, fluorescence yield, and X-ray excited optical luminance. Combined with an elliptically polarized undulator and the in situ conditions, the endstation can effectively perform X-ray magnetic circular and linear dichroism experiments in the soft X-ray range between photon energies of 250 and 2000 eV.